Process for manufacturing screws and a device for actuating the process

ABSTRACT

A device for manufacturing a screw ( 2 ) comprises a cylindrical support ( 3 ) having a horizontal axis (x-13 x)and being rotatable there about. A straight bar ( 7 ) is wound spirally about the support ( 3 ). The bar ( 7 ) is constrained to a guide ( 8 ) and can perform movements in a parallel direction to the axis (x—x) of the support ( 3 ) on command of a translator provided with an endless screw ( 14 ). The process for manufacturing the screw comprises controlling axial movement of the guide ( 8 ) in a predetermined rapport with the rotation of the support ( 3 ). The invention is particularly applicable in the manufacture of a screw for a screw conveyor.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the national stage under 35 U.S.C. 371 ofPCT/IT98/00276, filed Oct. 13, 1998.

TECHNICAL FIELD

The invention relates to a process for manufacturing screws and devicefor actuating the process. In particular, though not exclusively, theinvention relates usefully to a manufacturing process for production ofscrew-type conveyors.

BACKGROUND ART

The prior art teaches manufacturing processes in which a bar, generallystraight, flat and having a constant straight transversal section, iswound upon itself so as to form a relatively short spiral which is thenlengthened by traction force. The form of the screw thus obtained doesnot normally correspond to the desired shape, so that it usually has tobe re-worked by plastic deformation up until it reaches the desiredconformation. The above-mentioned adjustment phase must be performedwith considerable precision, and requires long and laborious workingtimes.

GB 242518 discloses a process for manufacturing a worm conveyorcomprising the following operations: fixing an end of a longitudinallyelongate body to an elongate support; commanding a rotation of tiresupport about a longitudinal axis of rotation thereof constraining tieelongate body to a guide arranged in proximity of tile support and ableto move in a parallel direction to a direction of the axis of rotationof tire support, the body winding spirally about the support by effectof a rotation of tile support and an axial movement of the guide.

EP 677711 discloses a process for manufacturing a freezing drumcomprising the winding of a metal strip on a cylindrical surface bydeformation of the strip from a rectilinear configuration to a helicalconfiguration driving an edge of the strip into tight contact with thesurface. The winding of the metal strip is performed by means of adevice equipped with means to make the surface rotate around its ownaxis while a couple of rollers drive the strip into tight contact withthe surface. The rollers are mounted on a movable block which translatesalong a direction parallel to the axis of rotation of the surface.

A further drawback in the prior art is the fact that manufacturingvariable-step screws involves a number of complications. This type ofscrew is produced, for example, by joining up one after another severallengths of screw having various steps. This is a complicatedmethodology, nor does it allow for production of screws withprogressively-varying steps, but only with discrete changes in step.

The main aim of the present invention is to obviate the above-mentionedlimits and drawbacks in the prior art by providing a process whichadvantageously enables screws to be manufactured simply andeconomically, especially those screws destined to be used as conveyors.

A further advantage of the invention is to reduce considerably themanufacturing times for the screws.

A still further advantage is the extreme precision and constancy of theresults obtained using the process in line with the nominal dimensionsof the design specifications, especially concerning the screw step.Furthermore, the invention enables very precise screws to be obtained,whatever the material the screw is made of.

A further advantage of the screw is to enable variable-step screws to bemade which are relatively simple and economical.

A further aim of the invention is to manufacture a constructionallysimple and economical device for carrying out the above-describedprocess.

DISCLOSURE OF INVENTION

These aims and advantages and more besides are all attained by theinvention, as it is characterised in the appended claims.

Further characteristics and advantages of the present invention willbetter emerge from the detailed description that follows of a preferredbut non-exclusive embodiment of the invention, illustrated purely by wayof a non-limiting example in the accompanying figures of the drawings,in which:

FIG. 1 is a schematic view from above of a device made according to thepresent invention during its functioning cycle;

FIG. 2 is a lateral view from below of FIG. 1;

FIG. 3 is an enlarged detail of FIG. 1, with some parts removed betterto evidence others;

FIG. 4 is the detail of FIG. 3 in a different operative configuration;

FIG. 5 schematically shows the view of FIG. 2, evidencing two differentpossible operative configurations assumed by the means for guiding thelongitudinal body destined to form the screw.

With reference to the above-mentioned figures, 1 denotes in its entiretya device for manufacturing a screw 2, for example for use as a screwconveyor.

The device 1 comprises a winder support 3, constituted in the example bya cylindrical support, having a longitudinal axis x—x which is arrangedhorizontally.

The cylindrical support 3 constrained at both ends by two opposite heads4 and 5 of a horizontal-axis chuck driven by an electric motor 6. Thesupport 3 can rotate on command about its own longitudinal axis x—x,with controlled and adjustable speed.

An end 7 a of an elongate body is removably constrained to thecylindrical support 3. The body 7 is destined to wind spirally about thesupport 3 to produce a screw 2. The body 7 is constituted in the exampleby a flat rectangular bar with a straight constant transversal section.In the example the bar, before being spiral-wound about the support, isstraight. The removable fixture of the end 7 a of the body to therotating support 3 can be realised, for example, by means of one or morescrew-type constraints. The figures show that the bar is fixed to thesupport with the flat part arranged perpendicularly with respect to theexternal surface of the support itself.

The device 1 comprises a mobile group, denoted in its entirety by 16,which can move in a horizontal direction parallel to the axis x—x of thesupport 3 in both directions. The mobile group 16 bears a guide 8,situated in proximity of the support 3, to which the body 7 isconstrained before being wound about the support. The guide 8 comprisestwo rotatable pulleys 9 each of which exhibits at its periphery a gulletwithin which the body 7 can roll. The two pulleys 9 are mounted on asupport body 10 and can rotate idle about two respectively parallelrotation axes. The two pulleys 9 are substantially coplanar and arealigned one after another so as to guide the body 7 destined to bescrew-formed. The inclination of the guide direction with respect to therotation axis x—x of the support 3 is variable on command. Alpha denotesthe angle formed by the guide direction vector and axis x—x. The guide 8further comprises a pressor organ 11, constituted in the example by ahydraulic cylinder, which presses the body against the pulleys 9 so asto hold it in position, especially during its winding about the support3. Other types of guides might be used, conformed and arranged so as toguide the body 7 according to a predetermined guide direction and tospiral-wind it about the support 3.

The mobile group 16 comprises a mobile base 12, mobile in a paralleldirection which is parallel to the longitudinal axis x—x of the support.The base 12 comprises a sliding carriage which runs on wheels along twostraight horizontal guides 13 arranged side-by-side at the oppositesides of the carriage. The support body 10 of the bar guide is rotatablycoupled to the base 12 and can rotate about a vertical axis.Furthermore, the guide group formed by the pulleys 9 and the pressor 11is rotatable on command with respect to the support body 10 about arotation axis which is parallel to the guide direction.

The guide 8 is thus able on command to make at least the followingmovements:

1) movements parallel to the longitudinal axis x—x of the supporttogether with the mobile group 16;

2) displacements with respect to the base 12 so as to vary the guidedirection, that is, the inclination with which the body is wound on thesupport 3, and therefore the step of the screw which is being formedaround the support 3.

These movements of the guide 8 with respect to the base 12 preferablycomprise rotations about at least one rotation axis. In the presentexample the guide 8 can rotate according to two non-parallel rotationaxes, in which: a first axis is orthogonal both with respect to theguide direction and to the support 3 rotation axis x—x; and a secondaxis is parallel to the guide direction. In the example the firstrotation axis of the guide is vertical; by effect of the guide rotationsabout the first rotation axis the angle alpha formed by the direction(variable) of the guide and the direction (fixed) of the rotation axisof the support 3 can be varied within an interval comprises, forexample, between 30 and 90 degrees. The controlled variation in thisangle alpha can also be performed during the winding phase of the body7, by means of control organs of known type and not illustrated, so asto obtain a variation in the screw step. In FIGS. 3 and 4 two differentpossible configurations of the guide means for the body 7 areillustrated, which can be achieved by rotation about the first verticalaxis of rotation.

FIG. 5 schematically illustrates two different configurations assumed bythe guide group by effect of rotations about the second rotation axis.These rotations cause variations in the angle beta formed by the planeincluding the pulleys 9 with a perpendicular plane to the rotation axisx—x of the support 3. The angle beta, which can preferably vary betweenzero and 30°, can be controlledly changed during the winding phase ofthe body 7, using, for example, a preset computer program.

The movements of the guide 8 with respect to the base 12 can be made,for example, by a coupling comprising a ball-socket joint or equivalentcoupling. The control of these displacements during the winding phase ina succession of predetermined displacements means that screws of extremeprecision can be obtained. This succession of displacements can bedecided according to many different criteria, for example the type ofmaterial the body 7 is made of.

The device 1 is preferably but not necessarily provided with means forcommanding and controlling the axial movement of the guide 8. The meansfor commanding and controlling act on means for translating the guidecarriage in a parallel direction to support 3 axis. The activation ofthe means for translating is connected to the means for commanding therotation of the support 3. In the illustrated example the means fortranslating comprise an endless screw 14 driven by an electric motor 15and coupled to the group 16 supporting the guide 8.

The motor 6 rotating the support 3 is provided with sensors fordetecting the angular position and rotation speed thereof The sensors,which might comprise. for example, a encoder (not illustrated), sendsignals to a unit of control and command of the device (not illustrated)which processes the signals using a special program and consequentlycontrols the motor 15 activating the translator of the mobile group 16.The group 16 can thus be advanced controlledly during the windingoperation of the body 7 about the rotating support 3, so that theadvancement can be correlated with the rotations of the support 3.

The unit for controlling and commanding can change the inclination ofthe guide 8 about the two rotation axes, in order to vary angles alphaand beta. By regulating the alpha and beta inclinations of the guide 8of the body 7 during the winding operation, continuously-variable-stepscrews can be produced.

Furthermore, the possibility of regulating inclinations alpha and betaenables the flat part of the body to be maintained at the desiredinclination (generally perpendicularly) to the axis x—x of the support3, both during and subsequent to winding.

The group 16 advancing program, which also controls the variousdisplacements of the guide 8 of the body 7, can be reprogrammedaccording to needs, for example in accordance with the type of screw tobe manufactured or the material the screw is made of.

During functioning, the end 7 a of the body is fixed to the support 3.The orientation of the body 7 is predetermined with relation to the axisx—x of the support 3, specially positioning the guide 8 so that theangles alpha and beta are at the predetermined values. The support 3 isthen rotated by means of the motor 6, generally at a constant velocity.The rotation of the support 3 winds the body 7 spirally and commands theaxial displacement of the guide group 16 in the direction denoted byarrow F.

Where the group 16 is not provided with its own motor but is, forexample, freely slidable on the guides 13, its axial displacement isdetermined by the rotation of the support 3 due to the rigidity of thebody 7 and the arrangement of the body in relation to axis x—x. In otherwords, the group 16 is drawn into axial displacements by the body 7itself as it moves.

Where the mobile group 16 is controlledly axially displaced by its ownmotor, the activation of the latter is made to coincide with the support3 rotation. In the example, the movement of the mobile croup 16 issubordinated to the rotation of the support 3. It has been found thatrelating the advancement of the mobile group 16 to the support rotation3, according to a predetermined law and controlled by theabove-mentioned control unit, enables a screw 2 with precise dimensionsto be obtained, i.e. precise in relation to the design specifications,with no need for further adjustment.

Furthermore, the device of the invention enables a good production rateto be achieved, the manufactured screws being constant in dimensions andextremely precise in relation to the design specifications. In itsfunctioning, the device performs a process for manufacturing screwswhich comprises the following operations.

Firstly, an end of a longitudinally elongate body is fixed to a support,also longitudinally elongate. The support is then rotated about its ownlongitudinal axis after first fixing the body to a guide arranged inproximity of the support, which guide can move in a parallel directionto the rotation axis of the support.

During the rotation of the support the body spiral-winds about thesupport itself due to the effect of the rotation of the support and theaxial movement of the guide. During the rotation of the support, theaxial movement of the guide can be free or can be predeterminedlycommanded and controlled, according to the characteristics of the screwto be manufactured. In particular, the axial movement of the guide canbe subjugated to the rotation of the support so that the supportrotations and axial displacements of the guide are interconnected by apredetermined and preferably repeatable rapport.

In the above process, it is preferable that the body is constrained topass through the guide according to a guide direction whose inclinationwith respect to the axis of the support can be changed during the courseof the rotation of the support.

This change in inclination can be made by means of rotations of theguide about a rotation axis whose direction is transversal (preferablyperpendicular) with respect both to the guide direction and to thedirection of the longitudinal axis of the support.

Furthermore, the guide can also be rotated about a second rotation axis,preferably parallel to the guide direction. This rotation can also becommanded and controlled during the winding phase of the body.

What is claimed is:
 1. A process for manufacturing a screw, comprisingthe following operations: fixing an end (7 a) of a longitudinallyelongate body (7) to an elongate support (3) having a longitudinal axis(x—x); rotating the support (3) about the longitudinal axis (x—x);constraining the elongate body (7) to a guide (8) arranged in proximityof the support (3), guiding the elongate body toward the support in aguide direction while moving the guide in a direction parallel to thelongitudinal axis (x—x) of the support (3), and rotating the guide abouta first axis that is parallel to the guide direction for winding thebody spirally about the support (3) by effect of rotation of the support(3) and axial movement of the guide (8), wherein the guide direction hasan inclination to the longitudinal axis (x—x), and further comprisingchanging the inclination of the guide direction during the rotation ofthe support (3).
 2. The process of claim 1, wherein the movement of theguide (8) in the direction parallel to the longitudinal axis is linkedto the rotation of the support (3).
 3. The process of claim 2, whereinthe rotation of the support (3) and the axial movements of the guide (8)are reciprocally connected by a repeatable rapport.
 4. The process ofclaim 1, wherein said change of inclination is achieved by causing theguide (8) to rotate about a second axis that is transverse to both theguide direction and the direction of the longitudinal axis of thesupport (3).
 5. A device for manufacturing a screw, comprising: a motor(6) for rotating an elongate support (3) about a longitudinal axis (x—x)thereof and an end (7 a) of an elongate body (7) being constrained tosaid support (3) to be wound spirally about said support (3)with aselected inclination as said support rotates; a guide (8), located inproximity of the support (3), for constraining the body (7), said guide(8) being able to perform movements in a parallel direction to thelongitudinal axis of rotation (x—x) of the support (3); a mobile group(16), on which said guide (8) is mounted, which is mobile in a paralleldirection to the longitudinal axis (x—x) of the support; wherein saidguide (8) is mounted for rotation in relation to the mobile group (16)about two non-parallel axes of rotation so as to vary the inclinationwith which the body (7) is wound about the support (3).
 6. The device ofclaim 5, comprising means for commanding said axial movement of theguide (8) in a predetermined rapport with the rotation of the support(3).
 7. The device of claim 6, wherein said means for commanding saidaxial movement of the guide (8) comprise a screw that is rotated in amanner bearing a selected relation to the rotation of the support (3).8. The device of claim 5, wherein said guide (8) is conformed andarranged so as to guide the longitudinal body (7) according to apredetermined guide direction and one of said two non-parallel axes ofrotation is parallel to tile guide direction.
 9. The device of claim 8,wherein the other one of said two non-parallel axes of rotation isperpendicular both to the guide direction and to the longitudinal axisof the support (3).
 10. The device of any one of claim 5, wherein saidguide (8) comprises at least one rotatable pulley (9) having a gullet ona periphery thereof, which gullet receives the body (7), and at leastone pressor (11) for pressing said body (7) against the pulley (9).